Certain types of pressure vessels are intended for exposure to elevated temperatures and require insulation during the elevated temperature use. For example, propellant positive expulsion tanks such as those used in the space shuttle and other liquid rocket vehicles, may be exposed to temperatures in excess of around 2000.degree. F. (about 1100.degree. C.) such as from pressurant gas during operation However, insulation attached to the tank will, at least in some applications, also be exposed to cryogenic temperatures during fabrication. ..For example, during a so-called "cryo-stretch" cycle, provision and positioning of suitable materials has been particularly difficult when the insulation is on a tank interior wall. In at least one tank configuration, the tank design is such that internal insulation must be applied to the tank wall prior to cryogenic pressurization. The tank may be filled with a pressurized cryogenic fluid and thus may be exposed to temperatures of about -320.degree. F. (about -200.degree. C.) or less. Previous materials which have been attempted for this purpose have generally been unable to survive cryogenic temperature exposure under pressure without unacceptable damage. Damage such as cracking of the insulated material and spalling has been observed. Cracking and spalling exposes at least portions of the tank in a substantially uninsulated condition. Accordingly, it would be advantageous to provide an insulation material for a tank which can withstand exposure both to pressurized cryogenic fluids and to gas at elevated temperatures.